1. Field of the Invention
The present invention relates to a voltage output circuit, more particularly to a dual voltage output circuit.
2. Description of the Related Art
Referring to FIGS. 1 to 3, a conventional dual voltage output circuit is used as an output buffer of a pixel circuit controller for application to a Liquid Crystal Display (LCD) 13 and is for generating two pixel-control voltages to control operations of pixel circuits of the LCD 13. The dual voltage output circuit includes first and second differential driving units 11, each of which includes an input stage 111, an intermediate stage 112, and an output stage 113.
The input, intermediate, and output stages 111, 112, 113 of each of the first and second differential driving units 11 are adapted to receive first and second operational voltages VA1, VA2, and cooperate to generate a respective one of first and second output voltages Vy1, Vy2 from a respective one of first and second pairs of input voltages (Vx1+, Vx1−), (Vx2+, Vx2−). It is to be noted that each of the first and second differential driving units 11 operates independently of the other.
The first and second differential driving units 11 are coupled to the LCD 13 via a switching circuit 14. The switching circuit 14 receives the first and second output voltages Vy1, Vy2 from the first and second differential driving units 11, and outputs the first and second output voltages Vy1, Vy2 to the LCD 13 in an alternating manner so as to prevent liquid crystals of the LCD 13 from being damaged by the ion effect.
Furthermore, referring to FIG. 4, the dual voltage output circuit further includes a bias voltage unit 12, which is operable to generate first and second bias voltages VBA, VBB from the first and second operational voltages VA1, VA2, and which is coupled to the intermediate stages 112 of the first and second differential driving units 11 for providing the first and second bias voltages VBA, VBB thereto so as to drive operations thereof.
However, a major drawback of the configuration of the aforesaid dual voltage output circuit is that changes in the first and second pairs of input voltages (Vx1+, Vx1−), (Vx2+, Vx2−) result in changes of the first and second output voltages Vy1, Vy2. Subsequently, upon completion of a successive switching of the first and second output voltages Vy1, Vy2 by the switching circuit 14, more current is drawn from sources of the first and second operational voltages VA1, VA2 due to the difference in numbers of electric charges at the first and second output stages 113.